Booster with spring to adapt air spring pressure for load dependent shock absorber

ABSTRACT

A suspension system for a vehicle includes a frequency dependent damper (FDD) or shock absorber defining a first pressurized working chamber and an air spring assembly defining a second pressurized working chamber. A booster enables pressure communication between the first pressurized working chamber and the second pressurized working chamber. The booster includes a resilient member that effects booster performance.

FIELD OF THE INVENTION

The present invention relates to frequency dependent damper s or shockabsorbers, and more particularly to a booster to adapt air springpressure for a load dependent shock absorber.

BACKGROUND OF THE INVENTION

Shock absorbers are used in conjunction with automotive suspensionsystems to absorb unwanted vibrations which occur during driving. Toabsorb these unwanted vibrations, shock absorbers are generallyconnected between the sprung portion (body) and the unsprung portion(suspension) of the automobile. A piston is located within a pressuretube of the shock absorber and the pressure tube is normally attached tothe unsprung portion of the vehicle. The piston is normally attached tothe sprung portion of the vehicle through a piston rod which extendsthrough the pressure tube. The piston divides the pressure tube into anupper working chamber and a lower working chamber. The shock absorber,by restricting fluid flow between the upper and lower working chambers,produces a damping force that counteracts the vibration that wouldotherwise be transmitted from the unsprung portion of the vehicle to thesprung portion of the vehicle.

Spring devices are implemented with the shock absorbers to resilientlysupport the vehicle on the suspension system. Exemplary spring devicesinclude coil springs, torsion bars and air springs. As the vehicle loadincreases the spring devices compress. The dampening capability of theshock absorbers, however, remains constant regardless of the vehicleload. While a constant dampening ability may be acceptable in someapplications, other applications would benefit from a shock absorberwhose dampening characteristics vary with vehicle load.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a suspension system for avehicle, which includes a shock absorber with variable dampeningcapability. The suspension system includes a frequency dependent damper(FDD) or shock absorber defining a first pressurized working chamber andan air spring assembly defining a second pressurized working chamber. Abooster enables pressure communication between the first pressurizedworking chamber and the second pressurized working chamber. The boosterincludes a resilient member that effects booster performance.

In one feature, the booster includes a housing defining segmentedchambers and a piston assembly slidably disposed within the segmentedchambers.

In another feature, the piston assembly includes a first piston dividinga first segmented chamber and a second segmented chamber and a secondpiston interconnected with the first piston and dividing the secondsegmented chamber and a third segmented chamber. The first segmentedchamber is in fluid communication with the second pressurized workingchamber and the third working chamber is in fluid communication with thefirst pressurized working chamber. The first piston is of a largerdiameter than the second piston. The resilient member biases the firstpiston.

In still another feature, a restrictor is disposed between the airspring assembly and the booster to inhibit pressurized fluid flowtherebetween.

In yet another feature, the booster includes a housing defining achamber and a piston slidably disposed within the chamber to definesegmented chambers. The resilient member biases said piston.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a vehicle having a suspensionincorporating frequency dependent dampers according to the presentinvention;

FIG. 2 is a cross-sectional side view of an integrated shock assemblyincluding a frequency dependent damper and an air spring assembly;

FIG. 3 is a schematic view of the suspension including the frequencydependent damper, air spring assembly and a booster according to thepresent invention; and

FIG. 4 is a schematic view of the suspension including the frequencydependent damper, air spring assembly and an alternative boosteraccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring now to FIG. 1, a vehicle 10 includes a rear suspension system12, a front suspension system 14 and a body 16. The rear suspensionsystem 12 includes a pair of independent suspensions 18 supporting apair of rear wheels 20. Each rear independent suspension 18 is attachedto the body 16 by means of a frequency dependent damper or shockabsorber 22 and an air spring assembly 24. Similarly, the frontsuspension system 14 includes a pair of independent suspensions 26supporting a pair of front wheels 28. Each independent front suspension26 is attached to the body 16 and includes an integrated shock assembly30 having the shock absorber 22 and an air spring assembly 24.

The shock absorbers 22 dampen the relative movement of the unsprungportion (i.e., the front and rear suspension systems 12 and 14) of thevehicle 10 with respect to the sprung portion (i.e., the body 16) of thevehicle 10. While the vehicle 10 has been depicted as a passengervehicle having independent front and rear suspensions, the shockabsorbers 22 and air spring assemblies 24 may be incorporated into othertypes of vehicles having other types of suspensions. It is alsoanticipated that the shock absorbers 22 and air spring assemblies 24 maybe incorporated into other types of applications, including, but notlimited to, vehicles having air springs, leaf springs, non-independentfront and/or non-independent rear suspension systems. Further, the term“shock absorber” as used herein is meant to refer to dampers in generaland thus includes MacPherson struts, spring seat units, as well as othershock absorber designs known in the art.

Referring now to FIG. 2, the integrated shock assembly 30 isillustrated. The integrated shock assembly 30 includes the shockabsorber 22 and the air spring assembly 24. The shock absorber 22 isdisclosed in detail in commonly assigned U.S. patent application Ser.No. 09/778,455, filed Feb. 7, 2001 and which is expressly incorporatedherein by reference. The shock absorber 22 includes a pressure tube 32,a piston assembly 34, a piston rod 36 and a rod guide assembly 38. Thepressure tube 32 defines a working chamber 40 that is filled with a gas,preferably air, at a specified pressure to act as the damping medium.The piston assembly 34 is slidably disposed within the working chamber40 and divides the working chamber 40 into an upper working chamber 42and a lower working chamber 44. A seal assembly 46 is disposed betweenthe piston assembly 34 and the pressure tube 32 to enable slidingmovement of piston assembly 34 within the pressure tube 32 withoutgenerating undue frictional forces. The seal assembly 46 seals the upperworking chamber 42 from the lower working chamber 44.

The piston rod 36 is attached to the piston assembly 34 and extendsthrough the upper working chamber 42 and through the rod guide assembly38, which closes the upper end of the pressure tube 32. The end of thepiston rod 36 opposite to the piston assembly 34 is secured to a sprungportion of the vehicle 10 via an upper mount assembly 48. The end ofpressure tube 32 opposite to the rod guide assembly 38 is closed by anend cap 50 that is connected to an unsprung portion of the vehicle 10.It is also anticipated that the piston rod 36 can be attached to theunsprung portion of the vehicle 10 and the end cap 50 attached to thesprung portion of the vehicle 10.

Referring now to FIGS. 2 and 3, the air spring assembly 24 of theintegrated shock assembly 30 comprises a flexible bladder 52 which issecured to the shock absorber 22 using a retainer 54 and which issecured to the upper mount assembly 48 by a retainer 56. The bladder 52defines chamber 58 that contains pressurized gas for supporting the body16 of the vehicle 10. The chamber 58 of the bladder 52 and the lowerworking chamber 44 of the shock absorber 22 are pressure-dependent onone another through a booster 60.

The booster 60 boosts the air pressure within the lower working chamber44 of the shock absorber 22. The booster 60 includes a housing 62 and apiston assembly 64 slidably disposed therein. The housing 62 defines aworking chamber 66 that is separated into a first working chamber 68, asecond or intermediate working chamber 70 and a third working chamber 72by the piston assembly 64. The piston assembly 64 includes a largediameter piston 74 slidably disposed in a first section 76 of thehousing 62 and a small diameter piston 78 slidably disposed within asecond section 80 of the housing 62. The large diameter piston 74 isconnected to the small diameter piston 78 by a piston rod 82.

The first working chamber 68 is in fluid communication with the chamber58 of the air spring assembly 24 through a conduit 84. The intermediateworking chamber 70 is in fluid communication with atmosphere through avent 86. The third working chamber 72 is in fluid communication with thelower working chamber 44 of the shock absorber 22 through a conduit 88.A restrictor 90 is optionally provided to restrict fluid flow throughthe conduit 84. The restrictor 90 inhibits dynamic interaction betweenthe air spring assembly 24 and the shock absorber 22. A resilient member92 is optionally provided to influence sliding movement of the pistonassembly 64. The resilient member 92 applies a reaction force againstthe piston assembly 64 as the piston assembly 64 compresses theresilient member 92.

For both the integrated shock assembly 30 and the separate shockabsorber 22 and air spring assembly 24, the air pressure within the airspring assembly 24 is lower than the pressure within the shock absorber22. The booster 60 enables boosting of the air pressure within the shockabsorber 22 and adjustment of the power dissipation ability of the shockabsorber 22 based on the load of the vehicle 10. As the vehicle load isincreased a load force F_(LOAD) acts on the air spring assembly 24 untila static state is achieved. F_(LOAD) increases the pressure (P_(ASA))within the air spring assembly 24. P_(ASA) acts across the surface area(A_(LDP)) of the large diameter piston 74 applying a force (F_(LDP)) andinducing movement of the large diameter piston 74. The large diameterpiston 74 moves until the static state is achieved.

As the large diameter piston 74 is caused to move, the small diameterpiston 78 correspondingly moves. The pressure (P_(LWC)) within the lowerworking chamber 44 acts across the surface area (A_(SDP)) of the smalldiameter piston 78. Thus, prior to achieving the static state, the smalldiameter piston 78 is caused to move and P_(LWC) increases.Additionally, as the large diameter piston 74 moves, it contacts theresilient member 92, compressing the resilient member 92. Upon achievingthe static state the forces are balanced across the piston assembly 64to provide:F _(LDP) =F _(SDP) +F _(RES)   (1)where: F_(LDP)=the force acting on the large diameter piston 74;

-   -   F_(SDP)=the force acting on the small diameter piston 78, and    -   F_(RES)=the force acting on the large diameter piston 74 by the        resilient member 92.

The pressure forces can be expressed in terms of P_(ASA) and P_(LWC) andthe resilient member force in terms of its spring rate (k) to provide:P _(ASA) A _(LDP) =P _(LWC) A _(SDP) +kx   (2)where: x=the distance the resilient member 92 has been compressed.

A_(LDP) can be expressed as a multiple of A_(SDP). This relationship isexpressed as:A _(LDP) =nA _(SDP)   (3)where: n>1.

Combining equations 2 and 3 provides: $\begin{matrix}{{P_{LWC} = {{n\quad P_{ASA}} - \frac{kx}{A_{SDP}}}}{{where}\text{:}}{\frac{kx}{A_{SDP}} = {{the}\quad{pressure}\quad{relieved}\quad{by}\quad{F_{RES}.}}}} & (4)\end{matrix}$

Thus, the booster 60 multiplies P_(ASA) by the factor n and applies thatpressure to the lower working chamber 44 as P_(LWC) minus the pressurerelieved by F_(RES).

P_(ASA) can be expressed as a function of F_(LOAD) according to thefollowing: $\begin{matrix}{P_{ASA} = \frac{F_{LOAD}}{A_{ASA}}} & (5)\end{matrix}$where: A_(ASA)=the total surface area of the bladder 52 over whichP_(ASA) acts.

Equation 5 can be integrated into equation 4 to provide: $\begin{matrix}{P_{LWC} = {{n\quad\frac{F_{LOAD}}{A_{ASA}}} - \frac{kx}{A_{SDP}}}} & (6)\end{matrix}$

Equation 6 illustrates that P_(LWC) is a proportional to F_(LOAD) andtherefore, the dampening power of the shock absorber 22 is dependent onF_(LOAD).

Referring now to FIG. 4, an alternative booster 60′ is illustrated. Thebooster 60′ adapts the air pressure within the chamber 58 of the airspring assembly 24 and the air pressure within the lower working chamber44 of the shock absorber 22. The booster 60 includes a housing 62′ and apiston 64′ slidably disposed therein. The housing 62′ defines a workingchamber 66′ that is separated into a first working chamber 68′ and asecond working chamber 70′ by the piston 64′. A resilient member 92′ isdisposed within the first working chamber and biases the piston 64′.More specifically, the resilient member 92′ maintains the piston 64′ ina neutral position when the vehicle 10 is unladen.

The first working chamber 68′ is in fluid communication with the chamber58 of the air spring assembly 24 through the conduit 84. The secondworking chamber 70′ is in fluid communication with the lower workingchamber 44 of the shock absorber 22 through the conduit 88. Therestrictor 90 is optionally provided to restrict fluid flow through theconduit 84. The restrictor 90 inhibits dynamic interaction between theair spring assembly 24 and the shock absorber 22.

In the unladen condition, the pressures and forces are static. Thisprovides a force balance across the piston, which can be expressed as:F _(FDD) =F _(ASA) +F _(RES)   (7)where: F_(FDD)=the force acting on the piston 64′ resulting fromP_(LWC);

-   -   F_(ASA)=the force acting on the air spring assembly 24; and    -   F_(RES)=the force acting on the large diameter piston 74 by the        resilient member 92.

Thus, when the vehicle is unladen, the pressure in the air springassembly 24 is lower than the pressure in the lower working chamber 44.As the vehicle is laden, P_(ASA) increases, resulting in movement of thepiston 64′ until a new static state is achieved. The force balance ofthe new static state is similarly expressed as:F _(FDD) =F _(ASA) +F _(RES)   (8)

Assuming the piston 64′ has moved enough where the resilient member 92′is no longer acting on the piston 64′, equation 8 can be expressed as:F_(FDD)=F_(ASA)   (9)

Equation 9 can be rewritten in terms of P_(ASA) and P_(LWC) to provide:P_(LWC)A_(PISTON)=P_(ASA)A_(PISTON)   (10)where: A_(PISTON)=the surface area of each side of the piston 94′.

As can be seen, when the vehicle is laden, P_(LWC) is equal to P_(ASA).

Implementation of the boosters 60 and 60′ between the air springassembly 24 and the shock absorber 22 enables a load dependent shockabsorber 22. More specifically, the power dissipated by the shockabsorber 22 is a function of the static pressure therewithin. The airpressure within the air spring assembly 24 is proportional to the loadof the vehicle 20. The booster 60 enables use of the air pressure withinthe air spring assembly 24 to adapt the pressure within the shockabsorber 22.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A suspension system for a vehicle, comprising: a frequency dependentdamper defining a first pressurized working chamber; an air springassembly defining a second pressurized working chamber; and a boosterenabling pressure communication between said first pressurized workingchamber and said second pressurized working chamber, said boosterincluding a resilient member that effects booster performance.
 2. Thesuspension system of claim 1 wherein said booster comprises: a housingdefining segmented chambers; and a piston assembly slidably disposedwithin said segmented chambers.
 3. The suspension system of claim 2wherein said piston assembly comprises: a first piston dividing a firstsegmented chamber and a second segmented chamber; and a second pistoninterconnected with said first piston and dividing said second segmentedchamber and a third segmented chamber.
 4. The suspension system of claim3 wherein said first segmented chamber is in fluid communication withsaid second pressurized working chamber and said third working chamberis in fluid communication with said first pressurized working chamber.5. The suspension system of claim 4 wherein said first piston is of alarger diameter than said second piston.
 6. The suspension system ofclaim 3 wherein said resilient member biases said first piston.
 7. Thesuspension system of claim 1 further comprising a restrictor disposedbetween said air spring assembly and said booster to inhibit pressurizedfluid flow therebetween.
 8. The suspension system of claim 1 whereinsaid booster comprises: a housing defining a chamber; and a pistonslidably disposed within said chamber to define segmented chambers. 9.The suspension system of claim 8 wherein said resilient member biasessaid piston.
 10. A suspension system disposed between a sprung portionand an unsprung portion of a vehicle, comprising: a frequency dependentdamper defining a first pressurized working chamber; an air springassembly integrated with said shock absorber and defining a secondpressurized working chamber; and a booster enabling pressurecommunication between said first pressurized working chamber and saidsecond pressurized working chamber, said booster including a resilientmember that effects booster performance.
 11. The suspension system ofclaim 9 wherein said booster comprises: a housing defining segmentedchambers; and a piston assembly slidably disposed within said segmentedchambers.
 12. The suspension system of claim 11 wherein said pistonassembly comprises: a first piston dividing a first segmented chamberand a second segmented chamber; and a second piston interconnected withsaid first piston and dividing said second segmented chamber and a thirdsegmented chamber.
 13. The suspension system of claim 12 wherein saidfirst segmented chamber is in fluid communication with said secondpressurized working chamber and said third working chamber is in fluidcommunication with said first pressurized working chamber.
 14. Thesuspension system of claim 13 wherein said first piston is of a largerdiameter than said second piston.
 15. The suspension system of claim 12wherein said resilient member biases said first piston.
 16. Thesuspension system of claim 9 further comprising a restrictor disposedbetween said air spring assembly and said booster to inhibit pressurizedfluid flow therebetween.
 17. The suspension system of claim 9 whereinsaid booster comprises: a housing defining a chamber; and a pistonslidably disposed within said chamber to define segmented chambers. 18.The suspension system of claim 17 wherein said resilient member biasessaid piston.
 19. A vehicle, comprising: a sprung component; an unsprungcomponent; and a suspension system disposed between said sprung portionand said unsprung portion, said suspension system comprising: afrequency dependent damper defining a first pressurized working chamber;an air spring assembly defining a second pressurized working chamber;and a booster enabling pressure communication between said firstpressurized working chamber and said second pressurized working chamber,said booster including a resilient member that effects boosterperformance.
 20. The vehicle of claim 19 wherein said booster comprises:a housing defining segmented chambers; and a piston assembly slidablydisposed within said segmented chambers.
 21. The vehicle of claim 19wherein said piston assembly comprises: a first piston dividing a firstsegmented chamber and a second segmented chamber; and a second pistoninterconnected with said first piston and dividing said second segmentedchamber and a third segmented chamber.
 22. The vehicle of claim 21wherein said first segmented chamber is in fluid communication with saidsecond pressurized working chamber and said third segmented chamber isin fluid communication with said first pressurized working chamber. 23.The vehicle of claim 22 wherein said first piston is of a large diameterthan said second piston.
 24. The vehicle of claim 21 wherein saidresilient member biases said first piston.
 25. The vehicle of claim 19further comprising a restrictor disposed between said air springassembly and said booster to inhibit pressurized fluid flowtherebetween.
 26. The vehicle of claim 19 wherein said boostercomprises: a housing defining a chamber; and a piston slidably disposedwithin said chamber to define segmented chambers.
 27. The vehicle ofclaim 26 wherein said resilient member biases said piston.
 28. Thevehicle of claim 19 wherein said frequency dependent damper and said airspring assembly comprise an integrated shock assembly.